Alternator problem.. - Page 2 - PeachParts Mercedes-Benz Forum

daw_two · #16 01-06-2008, 09:56 AM

Quote:

Originally Posted by Ramblin

If you don't have the alternator checked by a charging system tester and determine how many amps you are putting out at load you are wasting your time..I believe most of your auto part stores have these and the test actually takes very little time. In my years in the auto repair business I saw alternators that work and put as little as 15 amps out at load. At that level the battery barely charges and many things can go wrong with the electrics in any car...Hope this helps...

I just went thru this on "Candy", 1985 300D (for sale). Here's how it went down:

Car would not start because dead battery.
Jumped car and drove a while.....then car would start; had battery and alternator tested --- battery is weak, needs charging ; alternator not charging.
Replaced alternator; let car sit a week; car would not start.
Jumped car and drove a while......then car would start; had battery and alternator tested ---- not able to test battery, charge battery and retest; alternator not charging. This is a brand new alternator!!!! What do you mean it is not charging? Well.....the only way we can really check it .....is for you to remove it and then we can "bench" test it.
Next day I borrow neighbor's battery charger. Charge battery and then drive to that zone place.
Had battery tested. During the test, technician is sure it is going to be okay. At the end of the test, ask for temperature, I could have asked them to use a lower temperature, but I said use option #3 for 70 degrees F. Battery fails test.
Buy battery ( 1000CA/850CCA ) and battery installation kit (if you want them to install it). Installed.
Car cranks fine.
Alternator tested. Alternator is putting out 85 amps.

So. Was the first alternator good or bad? Don't know, right? A weak or dead or failing cell in a battery is what I believe was Candy's situtation. I even suspected it but allowed the technician in the first test to convince me the battery was okay. Granted the alternator MIGHT have been failing, but I would bet anyone on here, the old alternator was okay. Of course, we won't ever know because I turned the thing in for the core charge.

My advice to you --- Do this, FIRST: Take battery, have it charged, and load tested.

#17 01-06-2008, 10:06 AM

Quote:

Originally Posted by Cervan

I checked the voltage output, it slumps to 13.84 when at idle, and spikes up to 14 when just above idle. i dont understand it >.<

If the voltage is holding at above 13.5, I don't understand why the indicator light would come on. Have you tried measuring the votlage with a bunch if electrical load (lights, blower, etc.)?

Ramblin · #18 01-06-2008, 05:30 PM

I do stand corrected in the fact that actually before testing of the alternator the fully charged battery should be also load tested to see if it shows defects. I have seen a battery that shows correct voltage and within 30 seconds drops down to 8 volts. We also should realize that although auto parts stores hire highly trained individuals for behind the counter I am sometimes suspect of the testing procedures and the results. More than once I saw a supposedly good charging system and battery be fouled up by bad cables and connections which really throws a monkey wrench in the soup...

Cervan · #19 01-08-2008, 02:56 PM

Quote:

Originally Posted by Ramblin

I do stand corrected in the fact that actually before testing of the alternator the fully charged battery should be also load tested to see if it shows defects. I have seen a battery that shows correct voltage and within 30 seconds drops down to 8 volts. We also should realize that although auto parts stores hire highly trained individuals for behind the counter I am sometimes suspect of the testing procedures and the results. More than once I saw a supposedly good charging system and battery be fouled up by bad cables and connections which really throws a monkey wrench in the soup...

ill test the battery with full load on it and see what its voltage is then (car not running of course) Ill report back.

Cervan · #20 01-08-2008, 05:20 PM

Quote:

Originally Posted by Cervan

ill test the battery with full load on it and see what its voltage is then (car not running of course) Ill report back.

Forget that guys, i just totalled the car, i hit some black ice and i jsut washed the car so the brakes were iced up and i hit a tree doing about 30 miles an hour. pushed the front apron into the front wheel. so i guess my alternator problem will have to wait until i fix the car problem.

daw_two · #21 01-08-2008, 05:41 PM

Hope you are okay.

If you end up parting out the car, I could use:

sun visors.
visor clips.
rear seat section with good net.

All in palamino.

Cervan · #22 01-08-2008, 05:44 PM

Quote:

Originally Posted by daw_two

Hope you are okay.

If you end up parting out the car, I could use:

sun visors.
visor clips.
rear seat section with good net.

All in palamino.

ha, its a 4speed with the rare sunroof visor, if i do part it out make sure to pm me with what you want.

patbob · #23 01-08-2008, 07:10 PM

Quick recap to see if I got any observatiosn wrong:
* light goes out when rev engine,
* light goes out when wipers start their intermittant cycle,
* replacement alt was fine for a few weeks, then problem returned,
* voltage bobbles up and down.

I'm thinking a fried rectifying diode, but an intermittant short is also possible (one would think such would pop a fuse or be very noticable, but still...)

Check the connectors down by the alt to make sure corrosion hasn't crept up into the wires. Clean the connector mating surfaces and reinstall with dielectric grease.

Since it sounds like replacing the alt fixed the problem temporarily, you might try reinstalling the old alt. Maybe it was fine and the cure was just the disruption in that part of the engine bay.

Subtle intermittant problems liek this are really annoying.. hope you find it.

redbaronph123 · #24 01-09-2008, 03:42 AM

that happened to my wagon recently... bought new batt, but the light still was on and vanished when revved. Almost bought a surplus alternator to fix it, but in the end it was the mating of the terminal at the back of the alternator. Had the terminal replaced and rewired... all is well now.

Cervan · #25 01-18-2008, 07:46 PM

Found and fixxed this problem, (well wrecking the car fixed it.. but) I took the alternator off and inspected the brushes, Aha! they were down to little nubs.. but what threw me was that i just put brand new brushes in there, they were atleast two inches long.. And then i remembered what i did that night also.. I started the engine and took some emery cloth and scratched the stator while it spun (Trying to get any corrosion off of it) and it caused scratches on it wich wore them down so quickly.